1. Field of the Invention
The present invention relates to a chuck for a percussion tool such as, e.g., a hammer drill for receiving a working tool with a possibility of a limited axial displacement of the working tool within the chuck.
2. Description of the Prior Art
The chucks of the type described above have a working tool guide with radial guiding inner surfaces within which a shank of a working tool and the diameter of which corresponds to the inner diameter of the guide inner surfaces, is received with a possibility of a limited axial displacement. The axial displacement of the working tool, i.e., of the shank is limited from opposite sides by at least one rigid locking member which is axially secured in the chuck and engages in a radial outer locking groove provided in the shank and axially limited at its opposite sides. The chuck further usually includes at least one, projecting radially inwardly entraining web that engages in an associated, open at one of its axial ends, entrain groove formed in the shank.
German Publication DE-106 0 283 A1 discloses a chuck the locking members of which are formed by two, axially spaced, radially displaceable balls which are displaced between a radially outwardly release position and a locking position by two respective annular sleeves which are actuated by a common locking sleeve. The two locking members, which are formlockingly displaced by rotation of the locking sleeve, provided a combination chuck for different shank systems.
German Publication DE-44 00 779 A1 discloses a percussion power tool in which there is provided for the anvil which impacts an end surface of a working tool, a socket element formed as frictionally, axially displaceable sleeve in which the anvil is arranged with a possibility of a limited axial displacement. When a idle impact takes place, i.e., when the tip of the working tool does not contact a workpiece, the socket element is displaced axially forward and is frictionally retained in the idle stroke position outside of the impact region of the percussion piston. When the working tool engages the workpiece, the socket element, together with the anvil, is displaced again into its operational position within the impact region of the percussion piston. In the power tool of DE-44 00 779 A1, the prevention of an undesirable idle impact takes place within the percussion power tool itself.
An object of the present invention is to provide a chuck for a percussion power tool which would prevent the transmission of an idle impact of the power tool to the working tool.
Another object of the present invention is to provide a chuck for a percussion power tool which would prevent idle impacts in the power tool with an idle impact suppression, which could deactivate the idle impact suppression means within the power tool, particularly, when a heavy working tool is used and which is oriented vertically upward, as in this case, the gravity force of the working tool, deactivates the idle impact suppression means within the tool.
These and other objects of the present invention, which will become apparent hereinafter, are achieved by providing a chuck including at least one locking member for limiting an axial displacement of the shank to an axial displacement length from opposite sides, a displaceable stop member cooperating, within the shank displacement length, with a power tool side, stop surface of the shank, and al spring for biasing the stop member into engagement with the stop surface of the shank.
The displaceable stop member, which cooperates with the shank stop surface, additionally limits the displacement length of the shank to a partial length region which includes the front dead point so that the working tool occupies, with respect to the chuck, an idle impact position that is outside of the operational point of the power tool anvil. In this position, no impact is transmitted to the working tool during idle strokes of the power tool. Thus, even heavy working tools do not act on the idle stroke suppression means within the power tool.
Advantageously, the stop surface of the shank is formed by a portion of a power tool side, end surface of the shank. Thereby, conventional working tools having a shank associated with a specific chuck, can be used.
Advantageously, the stop member is arranged on a power tool side of the locking member in an axially spaced relationship relative thereto. This permits to form the stop surface or the power tool side, end surface of the shank.
Advantageously, the stop member is displaced in a radial direction against a biasing force of the spring between an inner radial stop formed by the working tool guide and facing a guide inner surface of the guide, with the inner radial stop formlockingly cooperating with the stop member, and an outer radial stop formed by the spring and which forcelockingly cooperates with the stop member. The inner and outer stops prevent the stop member from falling out, while the inner guide surface provides for positioning of the stop member.
Advantageously, the stop member is formed as a hardened ball having a diameter smaller than the locking member which, likewise, is formed as a ball. The smaller ball occupies less space. Further the ball-shaped stop member provides for a torsion-free point contact.
Advantageously, the stop member biasing spring is displaced, at least partially together with the locking member, and the chuck further comprises a manually displaceable, from outside, locking sleeve for displacing the spring, with the locking sleeve being displaceable axially or rotatably. The use of the locking sleeve permits to release and unlock the working tool in a single step. Thereby a user needs not to overcome the biasing force of the stop member-biasing spring when changing the working tools.
Advantageously, the spring has a radially outwardly extending cup that provides space for a free displacement of the stop member radially outwardly.
Advantageously, the stop member-biasing spring is formed as a ring spring that surrounds the stop member and is preloaded radially inwardly, with the ring forces providing for preloading of the spring.
Advantageously, the spring is supported, at least partially, on a cylindrical guide surface of the working tool guide which provides for a pivotal support of the spring.
Advantageously, the spring forms an axially projecting entraining hook formlockingly engageable in a recess of the at least partially pivotally displaceable, locking sleeve for joint rotation therewith. This permits to combine the stop member-biasing spring with the locking sleeve.
The novel features of the present invention, which are considered as characteristic for the invention, are set forth in the appended claims. The invention itself, however, both as to is construction and its mode of operation, together with additional advantages and objects thereof, will be best understood from the following detailed description of preferred embodiment when read with reference to the accompanying drawings.